Patent GB-351959-A (GB)
Title: Improvements relating to automatic and semi-automatic telephone systems
IPC: H04Q3/00
Filed: 1930-03-31
Abstract: 351,959. Automatic exchange systems. SIEMENS BROS. & CO., Ltd., Caxton House, Tothill Street, and TEES, J. E., 27, Elderslie Road, Eltham, both in London. March 31, 1930, No. 10183. [Class 40 (iv).] In selectors which search for a free outlet in a number of levels in succession, arrangements are provided so that the size of a group of outlets, .e.g. a group of PBX lines, is not restricted by virtue of the selector wipers reaching a limiting position without searching all possible outlets. When the wipers reach the limiting position they are released to normal and are then stepped to the first level of the switch bank and. searching continues over this and successive levels until a free outlet or the last outlet of a group is reached. The Figure shows a final selector for dealing with large groups of PBX lines and employing two sets of wipers and associated contact banks arranged in such a manner that search is effected in a level available to one set of wipers and if no free outlet is found, search is made in the same level by the other set of wipers. Detailed operation. When the selector is seized line relay A is energized and relays B, C are operated. Relay B busies the test wire c and in conjunction with C prepares the circuit of the vertical stepping magnet VM which in response to transmitted impulses operates the switch vertically to the corresponding level. Upon the termination of impulsing relay C releases and relay DR (1) operates to disconnect the vertical magnet VM and operate the rotary magnet RM to step the wipers into the bank. The wipers are rotated automatically and search takes place in the bank associated with wipers A, B, C, the wipers A<1>, B<1>, C<1> being at present ineffective. If a free outlet is found test relay H operates to open the rotary stepping circuit and mark the called line engaged at h<1>. If all the outlets traversed by wipers A, B, C are engaged the wipers are stepped on to the eleventh contacts and relays H, DR are operated over wiper C. Relay H prevents further operation of the rotary magnet RM and effects the operation of relay RN over wiper A to de-energize relay H and cause operation of the rotary release magnet RZM. The wipers are thus restored to rotary normal position and the contacts nrl de-energize relay RN and by reason of its slow release, relay E is operated to transfer the incoming leads from wipers A, B, C to wipers A<1>, B<1>, C<1>. De-energization of relay RN also causes operation of rotary magnet RM and search in the same level is effected by wipers A<1>, B<1>, C<1>. In the event that all the outlets associated with the second set of wipers are busy the wipers are stepped on to the eleventh contacts to operate relays H. DR over wiper C<1>. Relay H prevents further rotation and causes operation of relay VS over wiper AI. Relay VS releases E and RN is energized as in the case of unsuccessful search over the first set of contacts to cause operation of the rotary release magnet to restore the wipers. Upon restoration, relay RN is released and vertical magnet VM is operated to raise the wipers to the next level. Relay VS also is released and magnet RM is operated to move the wipers one step in the new level. Search then proceeds in the manner previously described. In the event that a group of outlets is extended to the first level, then, when all the outlets of all the levels containing lines of the original group have been tested and found engaged, the wipers A<1>, B<1>, C<1> reach a limiting position and are stepped on to the eleventh contacts to operate relays H, DR, RN as previously described. When the wipers reach the level containing the last of the original group of outlets normal post contacts np are opened so that upon operation of relay RN a short-circuit across relay F (11) is opened and the relay is operated to prepare circuit of release magnet ZM. Relay RN also causes release of H which effects operation of ZM and the selector is restored to normal. The off-normal contacts are restored, the vertical magnet VM being again operated to raise the wipers to the first level, and the relay VS being released to effect one rotary step after which search is effected in the manner already described. When a free outlet is found relay H operates to switch through the speaking leads. Relay DR releases and ringing generator RG is connected to line over relay F, ringing tone being applied to the calling line from RS. When the called subscriber replies relay F operates to switch through the calling lines and thereby effect operation of relay D which reverses connection to line relay A to give a supervisory signal. If all .the lines of the group are busy, stepping continues until the eleventh contact in the level in which the last line of the group is situated is reached. The eleventh contact of this level in the bank of wiper B<1> being earthed, relay BC operates over contacts s<1> which are operated by the switch when near the end of the levels. Lamp flash current and busy tone are fed alternately from wire BB to relay D and in the periods of lamp flash current, battery is fed over relay A to leads a, b in parallel to give the flash signal. A congestion meter may be connected to the eleventh contact of the level in which the last line appears, in which case relay BC closes a circuit over bc1, vs3 and wiper B for the meter. The release of the selector is effected when the incoming loop to relay A is opened, the relay A being disconnected from the line during release at contacts zm of the release magnet ZM. If there is a single large group of lines connected to the selector and occupying all levels the dotted connections Y instead of those marked X are used, the switch being adapted to search in the first level irrespective of the digit dialled. When the selector is seized relays A, B, C operate as before. Upon reception of the first impulse relay A relapses and operates the magnet VM to raise the switch to the first level. At the termination of the impulse, circuit is closed over contacts a1, vertical off-normal contacts n1, unoperated rotary off-normal contacts nr2, for relay DR, which opens circuit of vertical magnet to prevent the remaining impulses from taking effect. Upon release of relay C, rotary magnet RM is operated to step the switch into the bank after which auto. matic searching takes place in the manner previously described. If all the outlets are busy, the switch is returned to normal and restepped to the first level, after which search is again made over the outlets until a free line is found. Instead of a switch of the type in which the grouped contacts are arranged in horizontal levels vertically disposed, any two-motion type of selecting switch may be employed.